(1) Field of the Invention
The present invention relates to an apparatus and method for controlling synchronization in a system having a plurality of units when one of the units is disconnected from or connected to the system that is active.
(2) Description of the Prior Art
Generally, a system is comprised of a plurality of functional components, such as functional blocks, packages or printed circuit boards, and a plurality of functions of the system are respectively assigned to the functional components. Several systems are provided with a synchronization control capability that enables the operation of each of the units to be started and stopped in synchronism with each other if one unit is extracted from or inserted in the system that is active or powered ON. It is necessary that none of the functions of the system be considerably affected by the extraction of the unit or the insertion thereof when the system is active.
In the system of the type having a plurality of units to carry out a plurality of functions, each of the functions is accomplished by one unit independently of the other units. When one of the units is disconnected from or connected to the system that is active, it is necessary that the other units are reported of the connection or disconnection of the unit at the same time as the occurrence of the connection or disconnection. In addition, it is necessary to perform a resetting process for the unit or a function masking process for the other units at the time of the notification, in order not to considerably affect any of the other functions of the system.
Known synchronization control methods of the type described above are proposed in Japanese Laid-Open Patent Applications No.63-188287, No.2-297616 and No.4-58480.
In the proposed methods disclosed in the above-mentioned publications, a plurality of units are installed on a back wiring board (BWB) of the system by using multiple-pin connectors between the units and the BWB. In order to electrically connect the installed units to a system bus of the BWB, each unit is provided with a multiple-pin connector having long pins arranged in the connector center and short pins arranged at the connector end portions. In a case in which one of the units is extracted from the BWB, the disconnection of the unit (the stopped state) is reported to the other units of the system by turning OFF a signal path of a control signal sent to the other units when at least one of the short pins of the connector is not in contact with the BWB.
On the other hand, if the extracted unit is inserted in the BWB again, the connection of the unit (the operating state or the active state) is notified to the other units of the system by turning ON the signal path of the control signal when both the short pins of the connector come into contact with the BWB. In this manner, the conventional methods make it possible to extract one unit from the system or insert it without considerably affecting any of the other functions of the system.
However, one of the plurality of functions of the system is not necessarily assigned to a single component, and the system may carry out one function using a plurality of components in combination. Hereinafter, the plurality of components that carry out one of the functions with the units in combination are referred to as a combination of units.
For example, in a communication control system, one of several functions can be accomplished with a combination of a main processor unit and a main memory unit, and another function can be carried out with a combination of a main controller unit and a sub-controller unit. If one of such a combination of units is connected to the system but the other unit is disconnected or out of order, the system cannot suitably carry out the function which is assigned to the combination of units.
Therefore, if only one of the combination of units is connected to the system and the other unit is not connected thereto, the operating state of the unit and the stopped state of the other unit must be notified. If such a notification is not made, the system may operate incorrectly. For this reason, in a system having a plurality of units to carry out a prescribed function (one of several functions), it is necessary to carry out a synchronization control for the system which handles the notification of the operating state or stopped state of each unit to the corresponding unit. However, when the system has a large number of units to carry out the prescribed function or when several units are added or omitted, the hardware or the software needed to realize the above synchronization control will become complicated.